Base path customization for some pages (not the whole website)

[zwz]

Is your feature request related to a problem? Please describe.
I read https://sapper.svelte.dev/docs/#Base_URLs, it tells how to set base path for the whole website.
And I find that %sapper.base% in template.html is replaced by <base href="/"> by default.

But I want to customize the base path for some pages, for example, to shorten the img src.

Describe the solution you'd like
I tried to add in those pages

<svelte:head>
    <base href="/the-path-to-img-root/" />
</svelte:head>

But since the first base path (by %sapper.base%) takes effect, it does not work.

So I think maybe %sapper.base% should be commented out of template.html.
And all the href values in %sapper.styles% and %sapper.head% should start with %sapper.base%.

This would make base path customization for some pages possible by <svelte:head>.

How important is this feature to you?
I think this is quite important.
To shorten the src is just one example.
Since the path may contain params, it would be easier for the page to set the base path, and the components on this page has no idea of the params.

[Conduitry]

See #904. Sapper currently needs there to be a single site-wide base path, and we realize that's often inconvenient, but there are some hurdles to removing that requirement.